It has a catchment area of 930 square miles (2,409 km2), the largest in southern England. The map opposite shows only the major tributaries: a more detailed map[3] shows the extensive network of smaller streams feeding into the main river. Those tributaries rise from points along the North Downs, the Weald and Ashdown Forest.

Former minor tributaries include the Old Bourne River, that flowed through the Brook, Chatham (not to be confused with the main tributary River Bourne).[4]

The river and its tributaries flow through largely rural areas, Tonbridge, Maidstone and Medway being the exceptions. The Medway itself initially flows in a west-east direction south of the North Downs; at the confluence of the River Beult, however, it turns northerly and breaks through the North Downs at the Medway Gap, a steep and narrow valley near Rochester, before its final section to the sea.

Until 1746 the river was impassable above Maidstone. To that point each village on the river had its wharf or wharves: at Halling, Snodland, New Hythe and Aylesford. Cargoes included corn, fodder, fruit, stone and timber.

In 1746 improvements to the channel meant that barges of 40 long tons (41 t) could reach East Farleigh, Yalding and even Tonbridge. In 1828, the channel was further improved to Leigh. There are eleven locks on the river. The lowest, opened in 1792, is at Allington, and is the extent of tides. The others are East Farleigh, Teston, Hampstead Lane, Stoneham Old Lock (disused), Sluice Weir Lock, Oak Wier Lock, East Lock, Porter's, Eldridge's and Town Lock in Tonbridge. The locks will take craft up to 80 feet (24 m) by 18 feet (5.5 m), and vessels with a draft of 4 feet (1.2 m) can navigate the river. The shallowest point is just below Sluice Weir Lock which is prone to silting after heavy rain.[5]

Until recently the lowest crossing of the Medway was at Rochester, where there has been a bridge since Roman times. In the 14th century the Wardens and Commonalty of Rochester Bridge were instituted by Sir John de Cobham to pay for the rebuilding and upkeep of the bridge. Until 1963 the nearest crossing to Rochester Bridge was the 14th-century bridge at Aylesford, 12 miles (19 km) upstream. Since then the following additional crossings have come into use:

1963 A viaduct over the river was built south of Rochester to carry the first section of the M2 motorway. In 2003 this was widened to two separate spans.

Between 1963 and 1996 the M20 was built so a bridge by default was built over the Medway south of Aylesford.

1996 The Medway Tunnel became the river's lowest crossing, connecting Gillingham to Strood. The four-lane tunnel was constructed using the immersed tube method, and was partially paid for by Rochester Bridge Trust, the current form of the Wardens and Commonalty.

2003 A 0.8 miles (1.3 km) railway bridge, with a central span of 498 feet (152 m), was constructed for High Speed 1. The railway bridge lies parallel to the M2 motorway bridges.

Three other major crossings are at Tonbridge where bridges carry the A227 road and a rail link over the river, there is also a two-span viaduct which takes the A21 over the Medway Valley near Haysden.

The middle section of the Medway above Tonbridge, because of the many tributaries entering the river in this stretch, has always been subject to extensive flooding. Tonbridge itself has suffered frequent flooding over the centuries – so much so that the higher part of the town to north is called Dryhill. Flood protection measures have therefore had priority. In 1981, a flood barrier was constructed near Leigh to protect Tonbridge, which had been severely affected by the flooding of 1968. During periods of high flow, the downstream flow is controlled by allowing up to 1 square mile (2.6 km2) of farmland upstream of the barrier to flood.

In the eighteenth century Samuel Ireland published an illustrated book about a journey up the River Medway,[8] although he travels no further than the River Bewl at Bayham Abbey. The book contains a map, which shows some of the tributaries (unnamed). The illustrations of the river include the castles at Queenborough, Upnor, Leybourne, Tonbridge and Hever; Penshurst Place; and the bridges at Teston, Maidstone, Aylesford, East Farleigh, Barming, Branbridges and Tonbridge. The hop fields in the vicinity of the latter are also described; and the course of the River Len, which then supplied Maidstone with its water supply. The book states that Within about two miles of Tunbridge the Medway branches out into several small streams, five of which unite at the town")” ... having each its stone bridge.

Frindsbury Church above the former entrance to the Thames and Medway Canal

The Hartlake disaster of 1853 saw the deaths of 30 hop-pickers when a wagon carrying them crashed through the side of a rotten wooden bridge in Golden Green near Hadlow, throwing its passengers into the flood-swollen river.[9]

In 1942 the world's first test of a submarine oil pipeline was conducted on a pipeline laid across the Medway in Operation Pluto.

For the 1999 film The Mummy the river was filmed at Chatham Dockyard, in an imitation of a "port at Cairo". The scene is brief but involves the main protagonists departing on their mission to the city of the dead.

Every year a festival is held in Maidstone to celebrate the River Medway. Maidstone River Festival, which has been running since 1980, is held on the last Saturday of July. It features events on and around the river and attracts thousands to Kent's county town.[10] The Maidstone River Festival is celebrated during the last weekend in July every year. In 2009, the festival celebrated its 30th anniversary. The festival was cancelled in 2012 due to the London Olympics, but returned in 2013. However, the 2013 event did not include a funfair or a fireworks display as in previous years, and lasted just one day instead of two.

"Medway Flows Softly" is a song by local man George Gilbert; it was written in the mid 60s and is often played in local folk clubs and at festivals in Kent.

The River Medway is featured at Maidstone in the studio backdrop of the ITV1 regional news programme Meridian Tonight.

At 7.15 p.m. on 1 May each year, local morris dancers Kettle Bridge Clogs[11] dance across Barming Bridge (otherwise known as the Kettle Bridge) to mark the official start of their morris dancing season.

Recreationally the river is used by many. For example individuals and many clubs have trips to paddle along many different parts of the Medway (e.g. Bewl Canoe Club).[12] Individuals and clubs members paddling on the Medway and most other rivers should be members of the BCU.[13]

The Medway is said to divide the county of Kent into two parts: this may allude to the fact that, since AD 604, there have been two dioceses: Canterbury and Rochester, whose jurisdiction covered much of everyday life. The tradition has grown up, and today is kept alive by the Association of Men of Kent and Kentish Men, that those born in West Kent – the area north of the river, but including Maidstone, Gillingham (other than Rainham), Rochester and Chatham – are labelled Kentish Men (or Maids); while those born in East Kent are Men of Kent (or Maids). This labelling applies equally to those born in those parts of the traditional county absorbed into London in the 1880s.

Man has harnessed the power of the Medway for a millennium or more. Waterwheels and turbines powered by the waters of the Medway and its tributaries have been used by man to mill corn, make paper, make cloth, smelt iron, pump water and generate electricity. There are over two hundred sites on the Medway where such usage is known. Today, only one mill is working for a commercial trade.